This application pertains generally to the medical arts and more particularly to an improved self-occluding cannula assembly for insertion into blood vessels or various body cavities.
The invention is particularly applicable to flexible intravascular cannula of the type commonly used to administer intravenous infusions and/or to monitor pressures within arteries and/or veins of the human body. Accordingly, the invention will be described with particular reference to such applications. It must be appreciated, however, that the invention has utility in numerous other applications wherein it is desirable to prevent or limit back flow of bodily fluids from a tubular cannula. Examples of other types of cannula wherein the present invention may be utilized include, but are certainly not limited to; trocars for intra-abdominal or intra-thoracic insertion; long flexible catheters used for monitoring central venous pressures and for centrally administering drugs and various infusates; and various indwelling semi-permanent catheters such as the type commonly used in the administration of total parenteral alimentation.
Although many of the cannula in which the invention will be used may incorporate removable introducer needles or stylets to effectuate puncture of soft tissues, it must be further appreciated that the utility of the invention is not limited to such needle-bearing devices. In fact, the occluding means of the present invention may be employed with even the simplest types of medical tubing to prevent back flow of fluids therefrom.
It is common medical practice to insert tubular cannula into blood vessels for the infusion of various fluids and/or the monitoring of intravascular pressures. A basic intravenous cannula assembly of the prior art comprises a flexible cannula sheath having a rigid introducer needle positioned axially therewithin. The beveled tip of the hollow introducer needle extends a short distance beyond the distal tip of the cannula to permit easy penetration of the skin and underlying tissues. When the needle tip enters the target blood vessel, blood immediately fills the lumen of the needle and advances proximally to a transparent receptical on the needle hub where it may be readily viewed. Alternatively the needle hub may be connected to a syringe wherein a small amount of the blood may be visibly withdrawn into an existing quantity of saline solution. Thereafter the introducer needle is withdrawn. Thus, the cannula sheath remains in place as a means for subsequent infusion of intravenous fluids and/or monitoring of intravascular pressures.
Because the flexible cannula sheath comprises a generally hollow tube, blood will rapidly back flow (i.e. flash back) through the inner lumen of the cannula upon withdrawal of the introducer needle. As a result, a certain amount of blood invariably flows out of the proximal end of the cannula immediately after withdrawal of the introducer needle. Regardless of how adept the user may be at attaching an appropriate solution administration line or other auxiliary tube to the proximal end of the cannula, a certain amount of blood loss is likely to occur.
Likewise, if the attendant solution administration line or other tube subsequently becomes disconnected from the cannula, blood will immediately back flow from the cannula and may continue to flow therefrom until the disconnected line has been discovered and reconnected.
Indeed, any unnecessary back flow of blood from the cannula lumen is undesirable from a standpoint of general hygiene as well as in view of the present potential for blood born disease transmission Serious diseases such as Hepatitis and Acquired Immune Deficiency Syndrome are known to be transmissible to health care workers and others through contact with infectious blood.
A number of valving apparatus have been disclosed for selectively closing off and/or preventing back flow from intravenous cannula Many such valving apparatus comprise exteriorly mounted clamps, clips, compressors and other devices adapted to pinch off or otherwise prevent back flow from a catheter Additionally, a number of self-actuating or automatic valving members have been disclosed. Such self-actuating or automatic valving members are generally positioned within the bore of a cannula hub and purportedly function to prevent inadvertent back flow therefrom. Examples of self-actuating and/or automatic valving members of the prior art include those described in U.S. Pat. No. 3,620,500 (Santomieri), U.S. Pat. No. 4,143,853 (Abramson), U.S. Pat. No. 4,387,879 (Tauschinski), U.S. Pat. No. 4,512,766 (Vailancourt) and U.S. Pat. No. 4,683,916 (Raines).
Although the invention described in U.S. patent application Ser. No. 199,118 constitutes a significant advancement over the prior art, it has been found that certain embodiments of the elastic "obturator" member incorporated therein may be prone to inadvertent deformation whereby a portion of the obturator member may collapse into the proximal lumen of the frusto conical dilator projection during the movement of the obturator member from its initial "occluding" configuration to its "nonoccluding" configuration Such inadvertent deformation or collapse of the obturator member operates to obstruct the cannula lumen and interferes with normal operability of the cannula.
Accordingly, there has been identified a need in the art for further modifications and/or improvements of the self-occluding intravascular cannula assembly described in U.S. patent application Ser. No. 199,118.